Cancelling my 24 month phone contract

Hi there, 

I hope you can help me. I have a 24-month contract with o2 in Germany. It expires in September 2020. However, I moved back to Ireland a year ago and have since lost my German phone. I can no longer log in to my o2 account because I have no access to my phone or my texts and I can not see how much more I owe o2 or how much it costs to cancel.

I want to cancel my plan but how can I do this without having access to the lost phone?

Really need your help as I'm paying for a phone that I haven't used in months.

I have bills and contracts as proof.

Thanks for your help!